In some types of marine vessels, such as tug boats, for example, a high degree of maneuverability is very desirable for performing the intended function such as maneuvering large ocean-going liners into berth at the docks. For this reason, some tug boats are equipped with variable speed dual propellers mounted on respective drive shafts which are angularly positionable relative to each other in a horizontal plane to thereby provide precise maneuverability of the vessel. Conventional remote control apparatus for dual-propeller systems, above noted, are normally of the electrical type, which have been found objectionable at times because electrical fluctuations and outside disturbances may cause distorted operational effects. Moreover, electrical apparatus is costly and is more difficult to repair in case of failure.